1. Field of the Invention
The present invention relates to a damping material for attenuating vibrations by converting a vibrational energy to an electric energy. In particular, it relates to a piezoelectric dispersion type organic damping composite utilized for damping an apparatus or a device, absorbing noises and so on.
2. Discussion of Background
A conventional damping material is of such a type that a scale-like inorganic material such as mica is dispersed in a polymer matrix so that a vibrational energy is absorbed by mutual friction of the dispersed material, which is caused by vibrations, or of such a type that a magnetic interaction is utilized, in addition to the mutual friction, with use of powder of a magnetic material such as ferrite or the like. In either case of the conventional damping techniques, the loss factor tan .delta. is at most about 0.5.
Further, there has been proposed a technique of converting a vibrational energy to an electric energy by using powder of an inorganic ceramic piezoelectric as a dispersing material. In the proposed technique, however, the elastic modulus of the ceramics is far different from that of a polymer material whereby the effect of transmitting a kinetic energy is low: the anti-polarization factor is large as 0.3 because the shape of powdery particles is spherical to thereby reduce a strain-electric-conversion effect, and the loss factor tan .delta. is 0.5 or less.
As another proposal, a polymer in a gel state as a dispersing material is dispersed in a polymer matrix in an attempt that a vibrational energy is absorbed due to the friction between the gel-like polymer and the polymer matrix. However, the loss factor does not exceed 1. In particular, the damping material by the proposed technique can not be used as a structural material because it does not have a sufficient strength. In the above-mentioned conventional damping materials, the strain amplitude dependence is large since the kinetic interaction between the polymer matrix and the dispersing material is mainly utilized. Accordingly, although these damping materials provided a certain effect when the amplitude of vibrations was large ranging 10.sup.-3 -10.sup.-4, there exhibited less performance in a range of strain amplitude of 10.sup.-7 for the purpose of sound absorption and insulation.